An estimated 12 million tons of grain have been contaminated with copper, lead, mercury and other metals annually in recent years, the State Environmental Protection Administration said on its Web site.
The report didn't say whether any of the contaminated grain was consumed by people, and a SEPA spokesman, Zhang Shanling, declined to give any more details.
Pollution has become a prominent issue in China following a string of chemical spills in rivers that forced authorities to suspend running water to several major cities. The government also worries about pollution of farmland and severe smog in cities.
Leaders including Premier Wen Jiabao have called repeatedly for more stringent environmental protection. But officials often are reluctant to enforce rules that might hurt important local companies.
SEPA said it plans to spend 1 billion yuan (US$125 million; Ђ 100 million) by 2008 to carry out a nationwide study of farmland pollution.
Last year, China's grain production reached 484 million tons, up 3.1 percent from 2004, according to the government.
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